Viewpoints: Preparing for 3D Printing--When and How?

By Bill GibbsPresident/FounderGibbs and Associates, A Cimatron CompanyMoorpark, CAwww.gibbscam.com

Additive manufacturing, better known as 3D printing (3DP), is almost 30 years old. 3DP has become a catch-all phrase that encompasses over a dozen technologies that form parts through sequential, thin layer build-up of material. The mass media have grouped all 3DP machines, technologies, processes, and materials together, with a layman’s excitement that fosters the belief that 3DP can make anything, any time, in any size, in any quantity, from any material.

This inaccuracy has caused some anxiety for manufacturers. One way to understand “the state of the art” is to look at how the advantages and limitations of 3DP will fit into what you do. You probably work in metal, so I will focus on metal parts, although much of this applies to other materials as well.

I won’t go so far as to say there’s nothing to worry about, but if your business is making production parts, relax … and keep your eyes open. If you make plastic or conceptual prototypes, you are probably using 3DP already. If you make complex, working prototypes, you may be using high-end, metal-based 3DP machines, in combination with subtractive manufacturing, which we love and know as “machining.”

The greatest benefit of 3DP is its ability to build any shape you can model, including parts with complex internal features. Another benefit is that 3DP requires no tooling, i.e., no cutting tools and no workholding devices, eliminating what can be a great expense, because there is no stock to hold. There are no cutting forces acting on the part. No set up. The machines run untended, eliminating labor cost and the need for human presence.

All of those attributes make 3DP exciting and extremely attractive to design engineers, who would like nothing better than to design a part and print it, without having to know anything about manufacturing.

This could be of concern to a traditional manufacturer, were it not for 3DP’s limitations. The worst of these is speed. It is extremely slow, and time is money. Another hurdle is that material is limited to metal powders available. Don’t expect to get the same alloys you buy in sheet and billet. Metal 3DP is not simple. Sintering and metal melting 3DP have problems with warping, sagging, density, and mechanical properties.

Metal 3DP in production manufacturing represents the first step in a multi-machine process, perhaps replacing an initial casting. Most metal 3DP machines have closed controls, preventing direct programming from a CAM system, but providing programming input from an STL file. (In early CNC history, closed controls were common, and that limitation gave way to a proliferation of CAM software, providing greater functionality to all CNC machines.) Even if 3DP remains closed, there is still an important role for CAM software: For most applications, printed parts still need milling and turning to achieve adequate tolerances and surface finishes.

Let’s walk through an example. Your customer provides a solid model of a desired part, a turbine blade with complex internal cooling channels. You load the model into your CAM software and start modifying it for 3DP. You remove details not to be printed, like precisely drilled holes or tiny details. You add material to blade surfaces to allow for a finish-milling pass. You add some tabs to aid fixturing, then export an STL file for your metal 3DP machine and start printing. Meanwhile, your five-axis programmer uses the same CAM software, same finish-condition solid model and (initial condition) 3DP model to program finish-milling operations. The customer has an engineering change, and both the 3DP STL and five-axis part program update automatically from the new customer model: All processes are integrated within the same CAM software.

There is much to be said for metal 3DP. As engineers get more creative in using its capabilities in designs, more parts will require 3DP as a starting point because they can be made no other way. 3DP has a very long way to go before it replaces traditional machining, but if you want to bid on the next generation of complex parts, you may need to get involved sooner, and prepare for it now. Metal 3DP machines are getting faster and costs are coming down. The best you can do to prepare is ensure that you are using CAD/CAM software that provides the tools to support and integrate metal 3DP with the rest of your manufacturing processes. ME

This article was first published in the October 2013 edition of Manufacturing Engineering magazine. Click here for PDF.